This invention relates to cabinets, cases and other enclosures for housing sub-racks or card frames carrying circuit boards and/or modules carrying other electrical components. A cabinet or other enclosure including such sub-racks or card frames and/or modules will hereinafter, for convenience, be referred to as a "circuit board installation of the kind described".
The developement of silicon chips has resulted in a substantial increase in the component density of individual circuit boards and/or modules of a circuit board installation of the kind described and the increased component density of each circuit board and/or module of the installation has resulted in a greater power output and hence higher operating temperatures.
Conventional methods of controlling the temperature of the enclosure of a circuit board installation of the kind described include normal convection, forced convection, e.g. fan cooling, liquid cooling, various forms of heat conductor or sink, and a combination of two or more of these methods.
Where it is recognised that a substantial proportion of the heat is emitted by a particular individual electrical component within a circuit board installation of the kind described, it has been proposed to provide for local cooling of such an individual component, e.g. by directing pressurised cooling fluid towards such an individual component, and/or for local extraction of heat from such an individual component, e.g. by means of a thermally conductive module.
In one proposed arrangement for locally extracting heat from an individual electrical component of a circuit board installation of th kind described, there is thermally interposed between the component and a thermal conductor for conducting extracted heat to the environment externally of the enclosure of the installation, a thermally conductive module comprising a tubular housing made of a metal, metal alloy or other material of high thermal conductivity and closed at one end, and a spring loaded piston made of a metal or metal alloy of high thermal conductivity slidably mounted in and protruding from the tubular housing. The closed end of the tubular housing of the module is arranged in thermal contact with the thermal conductor and the exposed end face of the piston is urged by its associated spring into thermal contact with the individual component from which heat is to be extracted so that heat emitted by the component flows via the piston and tubular housing into the thermal conductor from where it is conveyed to the surrounding environment.
It is recognised that, unless the abutting surfaces of the component and the exposed end face of the piston are each substantially flat--and in many instances the component does not have a substantially flat surface--the efficiency of the heat transfer from the component to the spring loaded piston is unsatisfactory with the result that an undesirable proportion of heat emitted by the component is not extracted by the thermally conductive module.